This invention relates to a refractory material system for the wall of a cyclone separator and, more particularly, to such a refractory material system that has been provided with a surface that is resistant to erosion caused by particulate material.
Conventional cyclone separators, for service at ambient temperatures, are normally provided with a steel shell which may be lined with a relatively thick (4 to 6 inches) erosion-resistant refractory material, if severe erosion is expected. At high temperatures (up to about 1800.degree. F.) the lining may be provided with a dense, erosion resistant hot face refractory material and a lightweight, insulating back-up layer with an overall thickness of 12 or more inches. The purpose of the insulating back up layer is to insulate and protect the outer shell from hot, corrosive process gases as well as to provide an erosion-resistant, hot-face refractory material which can be repaired or replaced as erosion progresses.
A circulating fluidized bed boiler requires large diameter cyclone separators which are exposed to hot (1500.degree.-1800.degree. F.) gases containing erosive particles. Conventional thick refractory wall cyclone separators have several drawbacks for this application. The most significant drawbacks are that several inches of refractory material and insulation are required with a significant weight increase; the erosion-resistant layer must be resistant to rapid temperature changes which requires a special, costly, low-expansion refractory material and conservative heating cycles; the massive refractory material walls are difficult to install and maintain, especially in the roof sections; and frequent internal repairs are necessary to maintain the necessary surface contour and thickness. Any excessive loss of hot-face refractory material requires costly, time-consuming repairs to prevent overheating of the steel enclosure.
Cyclone separators having water-steam cooled walls have reduced heat loss through the enclosure walls. The cyclone walls, however, must be protected from erosion caused by hot, high-velocity fluid bed particles. A refractory system protecting the cyclone walls from erosion must have a predictable thermal conductance to prevent damage to the tubular water-steam walls in the event of a catastrophic shutdown in which the hot fluidized bed solids settle against the refractory system.
U.S. Pat. No. 4,635,713 discloses an erosion resistant tubular waterwall. The design criteria of a tubular waterwall, however, from the standpoint of erosion and thermal absorption characteristics differ substantially from the design criteria of the wall of a cyclone separator in a circulating fluidized bed boiler.
There is therefore a need for a lightweight hot-face refractory material system with high erosion-resistance a well as controllable and predictable thermal conductance to insure long term protection for the tubular support members and the steel enclosure during rapid shutdowns.